Lowering some recently raised expectations, a new study has found that megadoses of vitamin E don't prevent macular degeneration, the leading cause of blindness in Americans older than 55.

Many of the 6 million Americans with the disease, for which there is no cure, were encouraged last year when a National Eye Institute study showed that high doses of antioxidants, including vitamins E and C, beta carotene and the mineral zinc, can slow progression of the disorder in people with vision impairment by about 25%.

But new Australian research indicates that vitamin E alone does not prevent "either the incidence or progression of macular degeneration," said Hugh P. Taylor, a study coauthor and a professor at the University of Melbourne. In the study, published earlier this month in the British Medical Journal, 1,193 healthy volunteers between 55 and 80 were followed for four years. Half received daily supplements of 55 milligrams of vitamin E; the remainder were given a placebo, or dummy pill. At the end of the study there was no difference between the two groups, a result that researchers called "disappointing."

Still, NEI researchers aren't ready to write off vitamin E as a disease fighter. They point out that the Australian research involved only healthy subjects, only 1% to 2% of whom will go on to develop macular degeneration. Consequently, the sample size probably wasn't large enough to show preventive effects, according to Dr. Emily Y. Chew of the National Eye Institute in Bethesda, Md.

The 2001 NEI study, in contrast, involved 3,640 patients who already had moderate to severe macular degeneration, and several supplements were used. "The jury is still out on vitamin E alone," says Chew, who was that study's coauthor. "But the combination, which is proven to be beneficial for people with the disease, may be what's important."